#include <bits/stdc++.h>
#define ll long long
#define pii pair <int, int>
#define fi first
#define se second
#define pb push_back

using namespace std;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
const int N = 1e6+5, inf = 0x3f3f3f3f; 
int n, m, c, v[N], a[N], b[N];  
void solve () {
	cin >> n >> m >> c; 
	for (int i = 1;i <= n;i++) cin >> a[i]; 
	for (int i = 1;i <= n;i++) cin >> b[i];
	ll ans = 0; 
	for (int i = 1;i <= n;i++) {
		v[i] = min(b[i], m);
		ans += a[i]-v[i]; 
		m -= v[i]; 
		m += (a[i]-v[i])/c;  
	}
	cout << ans << "\n"; 
}

signed main () {
//	ios::sync_with_stdio(0);
//	cin.tie(0); cout.tie(0);
	int T = 1; cin >> T;
	while (T--) solve();
	return 0;
}